Effects of the source:sink ratio on the phenotypic plasticity of stem water potential in olive (Olea europaea L.)

The aims of this work were to quantify (i) the effect of the source:sink ratio on stem water potential (SWP) and (ii) the phenotypic plasticity of SWP and its relationship to oil yield components in olive. Trees with a 3-fold variation in the source:sink ratio (crown volume/fruit number per tree) were monitored in 2007–2008 and 2008–2009 in a fully irrigated orchard in Mendoza, Argentina. The combination of rainfall, irrigation, and evaporative demand led to a steady SWP largely above –1.65 MPa in 2007–2008 and a marked seasonal decline from –1.13 MPa to –2.04 MPa in trees with a medium and low source:sink ratio in 2008–2009. Plasticity was quantified as the slope of the norm of reaction for each trait. Across seasons, trees with a high source:sink ratio had a higher SWP than their counterparts with a medium and low source:sink ratio. Plasticity of SWP was highest in olives with a low source:sink ratio (slope=1.28) and lowest for trees with a high source:sink ratio (slope=0.76). The average SWP for each source:sink ratio and season was unrelated to both the source:sink ratio and yield components. On the other hand, the plasticity of SWP was positively associated with fruit number and negatively associated with the source:sink ratio, fruit weight, and fruit oil weight. The plasticity of the SWP was unrelated to SWP per se. It is concluded that understanding the effect of the source:sink ratio on plant water relations would benefit from a dual perspective considering the trait per se and its plasticity. A dual approach would also allow for more robust plant-based indicators for irrigation.EEA JunínFil: Trentacoste, Eduardo Rafael. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Junín; ArgentinaFil: Sadras, Victor Oscar. South Australian Research & Development Institute; AustraliaFil: Puertas, Carlos Marcelo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Junín; Argentin

Transpiration, transpiration efficiency and harvest index in sunflower (Helianthus annuus L.)

The following aspects of the water and carbon economies of sunflower (Helianthus annuus L.) were investigated: (a) the mechanisms that regulate evapotranspiration (ET) and the partitioning of ET between transpiration (T) and soil evaporation (E), (b) the intra-specific and intra-seasonal variations in transpiration efficiency (TE= biomass/transpiration), (c) the source-sink relationships between stems and reproductive structures, and (d) the physiological basis of the relationship between harvest index (HI) and the fraction of water transpired after anthesis (FTAA). A range of hybrids of different stature were compared in glasshouse and field conditions. It was established that: a) ET depended on both water regime and crop factors (e.g. leaf area index, LAI). The fraction of weekly ET due to soil evaporation ranged from 0.12 to 0.70. Transpiration per unit leaf area was smaller in shorter hybrids before anthesis. This was associated with smaller interception of radiation (IR) per unit leaf area. The regulation of transpiration, irrespective of cultivar, depended on the timing of water shortage. Lower IR (resulting from reduced expansion of leaf area) accounted for the smaller transpiration in crops stressed before anthesis. Transpiration of post-anthesis stressed crops was reduced by both smaller canopy conductance and smaller IR caused by greater leaf senescence. b) Post-anthesis radiation-use efficiency (RUE) was positively associated with an index of relative-sink demand (RSD = seed number/ intercepted radiation after anthesis). TE was, in turn, associated with RUE. Intraspecific differences in RUE (and TE) derived from differences in RSD caused by the low seed set of the semi-dwarf compared with the standard-height hybrid. TE was greater before than after anthesis. The smaller production value of biomass produced after anthesis was a major cause of the intra-seasonal variation in TE. Vapour pressure deficit also contributed to this variation. c) Apparent contribution of stem assimilate to seed yield varied with genotype. It is proposed that RSD modulates the mobilization of stem assimilate. d) A simple two-parameter model quantifying the responses of HI to FTAA is derived from physiological principles that account for (i) the relationship between biomass and transpiration and, (ii) the relationships between sources and sinks. The model performed well in tests against a wide range of data from wheat and sunflower. These tests also show the consistency of the physiological meaning attributed to the parameters of the model. The sensitivity of those parameters to both inter- and intra-specific variation is demonstrated. The model is proposed as a simple method to estimate grain yield of determinate species in conjunction with either photosynthesis- or transpiration-based estimates of biomass

Profiles of leaf senescence during reproductive growth of sunflower and maize

We investigated the effect of reproductive growth on the profiles of leaf senescence in maize (Zea mays L.) and sunflower (Helianthus annuus L.). Leaf senescence after flowering was assessed using both structural (leaf chlorophyll, nitrogen and dry matter) and functional (photosynthesis) variables in undisturbed plants (+G) and in plants in which grain set was prevented (-G). Two weeks after flowering, lack of grain accelerated senescence in maize and delayed senescence in sunflower as indicated by leaf chlorophyll; leaf nitrogen and dry matter were less sensitive response variables. Lack of interaction between reproductive treatment and leaf position indicates that the senescence signal, whatever its nature, was equally effective throughout the plant in both species. In both species, feedback inhibition of photosynthesis was first detected 30-35 d after flowering; excess carbohydrate in the leaves was therefore an unlikely trigger of accelerated senescence in maize. As reproductive development progressed, differences between +G and -G plants were more marked in sunflower, and tended to disappear or reverse in maize. In sunflower, interactions between leaf position and reproductive treatment - attributable to the local effect of grain - were detected around 20-27 d after flowering.Fil: Sadras, Victor Oscar. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Echarte, Laura. Universidad Nacional de Mar del Plata; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce. Área de Investigación en Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Andrade, Fernando Héctor. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Review: critical appraisal of methods to investigate the effect of temperature on grapevine berry composition

The grapevine is an economically important crop and a model species of long‐lived perennials widely used in bioclimatic studies. Ambient temperature modulates berry composition, hence the significant research effort in establishing links between temperature, berry composition and wine attributes. Our current understanding of the effect of temperature on berries and wines has been largely gained from indirect methods or direct methods in controlled conditions. Indirect methods include comparisons of thermally contrasting locations and vintages; this approach is of value but is bound to be inconclusive as the effect of temperature is often confounded with other weather and climate factors (solar radiation, vapour pressure deficit and rainfall), management practices and soils. Direct experimental methods comparing fruit grown at a range of temperature are required to prove cause‐and‐effect, but attempts to modify the thermal regime of the plant often generate secondary effects. Experimental artefacts in controlled environments often include small soil volume, lack of wind and altered radiation regimes, with direct implications for plant physiology and berry composition. Experiments involving controlled temperature in vineyards aim at a higher degree of realism, but are constrained by cost, issues of scale in space and time, and are not necessarily free from artefacts. Indirect and direct methods are of course non‐mutually exclusive but complementary. This review critically assesses the methods used to elucidate the effect of temperature on grape berry composition. It emphasises the limitations of studies where confounded effects are overlooked. With the focus on selected berry traits (total soluble solids, total and titratable acidity and anthocyanins), we analyse the dominant effect of temperature and highlight discrepancies and agreements between indirect and direct research methods.EEA MendozaFil: Bonada, Marcos. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Mendoza; Argentina. University of Adelaide. School of Agriculture, Food and Wine; Australia. South Australian Research & Development Institute; AustraliaFil: Sadras, Victor Oscar. University of Adelaide. School of Agriculture, Food and Wine; Australia. South Australian Research & Development Institute; Australi

How do phosphorus, potassium and sulphur affect plant growth and biological nitrogen fixation in crop and pasture legumes? A meta-analysis

Worldwide, legumes are grown on approximately 250 M ha and fix about 90 Tg of N2 per year. Plants involved in biological nitrogen fixation (BNF) are particularly sensitive to deficiencies of phosphorus (P), potassium (K) and sulphur (S). These nutrients can affect BNF directly; this is modulating growth of rhizobia, nodule formation and functioning, or indirectly by affecting the growth of the host plant. However, several process and mechanisms remain unclear. We compiled a data set (63 studies) on the effects of P, K, and S deficiency on shoot mass, nodule mass and number, nitrogenase activity (estimated by the acetylene reduction activity test, ARA) and the concentration of N, P, K and S in shoots and nodules. Our aims were (1) to compare the relative sensitivity of these traits to nutrient deficiency and (2) to probe for nutrient-specific patterns in trait responses. Our quantitative analysis confirms that nodule growth and number are more sensitive than shoot mass in response to deficiency of P, K and S. In addition, nodule activity decreases more than both shoot and nodule mass, which indicates a reduction in nodule productivity; this is likely related with direct effects of these nutrients on physiological and metabolic processes of nodules. The conserved shoot N concentration, in comparison to concentration of P, K and S indicates a relatively greater accumulation of N that matches the proposed N-feedback mechanism down-regulating BNF in nutrient-deficient systems. Despite some nutrient-specific differences, i.e. smaller nodules and higher N/K ratio with shortage of P and K, respectively, the patterns of growth, nodule activity and nutrient concentration were similar for all three nutrients P, K and S. This indicates that a unique mechanism could be depressing BNF (N-feedback) in conjunction with direct effects of the nutrients on nodule activity. Scarcity of data related to N, K and S concentration in nodules is a major constrain for deep analysis of the deficiencies of the nutrients. Critical concentrations of P, K and S in plant and nodule tissues are also a major gap. Models are needed that integrate the direct effect of the nutrients on nodule growth and activity with the N-feedback mechanism.Fil: Divito, Guillermo Adrián. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sadras, Victor Oscar. University of Adelaide; Australi

Independent genetic control of maize (Zea Mays L.) kernel weight determination and its phenotypic plasticity.

Maize kernel weight (KW) is associated with the duration of the grain-filling period (GFD) and the rate of kernel biomass accumulation (KGR). It is also related to the dynamics of water and hence is physiologically linked to the maximum kernel water content (MWC), kernel desiccation rate (KDR), and moisture concentration at physiological maturity (MCPM). This work proposed that principles of phenotypic plasticity can help to consolidated the understanding of the environmental modulation and genetic control of these traits. For that purpose, a maize population of 245 recombinant inbred lines (RILs) was grown under different environmental conditions. Trait plasticity was calculated as the ratio of the variance of each RIL to the overall phenotypic variance of the population of RILs. This work found a hierarchy of plasticities: KDR ≈ GFD > MCPM > KGR > KW > MWC. There was no phenotypic and genetic correlation between traits per se and trait plasticities. MWC, the trait with the lowest plasticity, was the exception because common quantitative trait loci were found for the trait and its plasticity. Independent genetic control of a trait per se and genetic control of its plasticity is a condition for the independent evolution of traits and their plasticities. This allows breeders potentially to select for high or low plasticity in combination with high or low values of economically relevant traits.Fil: Alvarez Prado, Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Departamento de Producción Vegetal; ArgentinaFil: Sadras, Victor Oscar. South Australian Research and Development Institute; Australia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Borras, Lucas. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Departamento de Producción Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentin

Functional crop types are more important than diversity for the productivity, profit and risk of crop sequences in the inner Argentinean Pampas

CONTEXT: Over the last 250 years, many natural ecosystems in South America, including the Inner Pampas of Argentina, evolved into extremely simplified agroecosystems. In the last 25 years, simplified soybean-based crop sequences have become widespread. Putative drivers of the wide adoption of this system include high soybean grain price, simplified agronomic management and low cost, but comparison of production, profit and risk in current and alternative crop sequences are lacking. OBJECTIVE: Our aim was to compare the production, profit, and risk of seven crop sequences varying in their diversity, cropping intensity and the proportion of functional crop types. METHODS: We modelled seven typical or feasible crop sequences for two locations with different rainfall and soil water holding capacity for a 50-yr period. Crop sequences included wheat (W) or fallow during winter and soybean (S) or maize (M) as single and double crops during summer, and were characterized with indexes of agrobiodiversity (ABDI, from 0.33 to 1.00), cropping intensity (from 0.40 to 0.83) and soybean proportion (SP, from 0 to 1.00). RESULTS AND CONCLUSIONS: W/M-M had the highest and S-S the lowest yield in both locations. The high yielding crop sequences had a lower stability of grain yield that those with a high proportion of soybean (S-S and W/S-S). Yield stability and CVaR (conditional value-at-risk) for gross margin and gross margin ratio were unrelated with ABDI. The prevalent, least diverse soybean monoculture (S-S) had the lowest cost and medium profit-risk metrics. Increasing the proportion of maize contributed to higher gross margin and gross margin ratio with a lower risk in some crop sequences. Crop sequences with high proportion of soybean (S-S and W/S-S) had low mean cost with a close to average CVaR. However, these were not the sequences with the highest gross margin or gross margin ratio. Our results demonstrated that functional crop types (cereal and legumes) were more important than diversity and cropping intensity for the profit and risk of crop sequences in the Inner Argentinean Pampas. SIGNIFICANCE: Economic risk-benefit analysis of crop sequences is necessary but not sufficient to understanding the drivers of grower's choices, which are greatly influenced by context regarding policies for grower support, taxes, and land ownership.EEA Marcos JuárezFil: Videla Mensegue, Horacio Rogelio. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Marcos Juárez. Agencia de Extensión Rural Laboulaye; ArgentinaFil: Caviglia, Octavio. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Caviglia, Octavio. Universidad Nacional de Entre Ríos. Facultad de Ciencias Agropecuarias; ArgentinaFil: Sadras, Victor Oscar. South Australian Research & Development Institute; AustraliaFil: Sadras, Victor Oscar. University of Adelaide. School of Agriculture, Food and Wine; Australi

Effect of irrigation and tree density on vegetative growth, oil yield and water use efficiency in young olive orchard under arid conditions in Mendoza, Argentina

We measured the effects of planting density (238, 317 and 476 trees ha−1), irrigation (fully irrigated control vs. deficit irrigation) and their interaction on the vegetative growth, yield and irrigation water use efficiency (IWUE) of young olive trees during three seasons. In the water deficit treatment, irrigation was applied when midday stem water potential (SWP) dropped below −2.5 MPa; SWP of controls was maintained between −1.2 and −1.5 MPa. Across irrigation treatments, oil yield at high density (968 kg ha−1) was 70 % higher than at low density. Reduction in oil yield due to deficit irrigation was not significant compared to control (501 vs. 664 kg ha−1). IWUE at lower tree density averaged 1.5 kg ha−1 mm−1, increased by 50 % in intermediate density and by 57 % at the highest density. Deficit irrigation increased IWUE twofold with respect to controls. IWUE responded to the interaction density × irrigation whereby the highest IWUE (4.6 kg ha−1 mm−1) was obtained at highest density and deficit irrigation. IWUE was nonlinearly related to seasonal water stress integral ( Sψ ), where maximum efficiency corresponded to 180 MPa days. The negative correlation between fruit water concentration and Sψ highlights the potential benefit of deficit irrigation of increasing oil extractability. The positive outcomes of increasing the density (higher oil yield) and deficit irrigation (higher IWUE, lower water concentration in fruit) need to be weighed against the long-term effect on vegetative growth. Under our conditions, three seasons of water deficit reduced crown and trunk size by 35 % in relation to fully irrigated.EEA JunínFil: Trentacoste, Eduardo Rafael. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Junín; ArgentinaFil: Puertas, Carlos Marcelo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Junín; ArgentinaFil: Sadras, Victor Oscar. South Australian Research & Development Institute; Australi

Reproductive partitioning and seed set efficiency in soybean, sunflower and maize

Seed number per plant (SNP) can be modelled as a function of plant growth rate during the critical period for seed set (PGRC), the proportion of plant growth partitioned to reproductive organs (PR) and the minimum assimilate requirement per seed (λ). In comparison to PGRC, less attention has been given to PR and λ. In this paper, we analysed reproductive partitioning and λ in three species of contrasting reproductive strategies, soybean (Glycine max L. Merrill), sunflower (Helianthus annuus L.) and maize (Zea mays L.). To study plant-to-plant variation and to characterise stability of the variables analysed, we focused on individual plants grown under a wide range of plant densities. In soybean and sunflower, reproductive partitioning comprised about 50% of shoot growth, was fairly stable in a wide range of plant growth, and only decreased in a few, very small plants. In comparison, reproductive partitioning in non-prolific maize showed an optimum, was generally below 50% and exhibited a strong variation and instability at plant growth rates ≅2 g/day. Among species, stability of reproductive partitioning correlated inversely with a PGRC threshold for reproductive growth and positively with reproductive plasticity at high PGRC. Consideration of reproductive partitioning improved estimation of seed number, particularly in maize, a species prone to barrenness. Seed number as a function of reproductive growth was adequately described through linear (soybean) and hyperbolic models with x-intercepts (sunflower and maize). Seed set efficiency in terms of seed number per unit of reproductive growth (Ef) was constant only in soybean. In sunflower and maize, Ef increased with decreasing reproductive growth and became highly variable and unstable when reproductive growth was close to the threshold for seed set. In maize, such threshold was higher than in soybean and sunflower possibly as a consequence of a higher minimum combined demand for assimilate, resulting from a higher λ and number of simultaneously developing sinks. Inclusion of parameters assessing (i) stability in reproductive partitioning at low plant growth rates, and (ii) the minimum assimilate requirement per seed might improve seed number estimation.Fil: Vega, Claudia Rosa Cecilia. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Andrade, Fernando Héctor. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sadras, Victor Oscar. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

N and S concentration and stoichiometry in soybean during vegetative growth: Dynamics of indices for diagnosing the S status

Information regarding the pattern of sulphur (S) accumulation in shoots is scarce for field crops and few comprehensive analysis were performed on N:S stoichiometry. Particularly, the need to study the patterns of uptake, allocation and stoichiometry of S and N in soybean is two-fold. First, the main areas for soybean production in the world have been recently reported as S-deficient. Second, S concentration (%S) and N:S ratios are relevant for diagnosing S deficiency. The aim of this work was to analyze, in a gradient of S availability, the dynamics of nitrogen concentration (%N), %S and N:S ratio in soybean lamina, stem and shoots during vegetative growth. Experiments were performed at Balcarce, Argentina during two growing seasons. Two soybean cultivars were evaluated: DM2200 (maturity group II) and DM4970 (maturity group IV), sown in optimum dates for the region (mid-November). DM2200 was also sown late (early January). We sampled crops between biomass ≈ 1 Mg ha−1 and R5. Shoots were separated in lamina, stem and petiole, and pod. The adjusted S dilution curve for S-sufficient treatments was attenuated in soybean (S = 2.8 W−0.11), with no differences among cultivars of maturity groups II and IV, and sowing dates from November to January. For the same treatments, the N:S ratio was stable in shoots during vegetative growth (N:S = 12.2), supporting the use of a unique threshold for diagnosing the S status during this period. Sulphur concentration in stems was more responsive to the availability of S than%S in lamina. In addition, the concentration of N in stem tended to be constant with variation in %S while %N and %S correlated in lamina. This produced a greater response of N:S in stem than in lamina. Thus, the determination of%S and N:S in stem are good candidates as indicators of S status of soybean.EEA BalcarceFil: Divito, Guillermo Adrián. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Echeverria, Hernan Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce-Unidad Integrada-Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Andrade, Fernando Hector. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce-Unidad Integrada-Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Sadras, Victor Oscar. South Australian Research & Development Institute; Australi